Organic Sonochemistry, ultrasonic acceleration of the reduction of simple and deactivated aryl halides using lithium aluminum hydride
✍ Scribed by Byung Hee Han; Philip Boudjouk
- Publisher
- Elsevier Science
- Year
- 1982
- Tongue
- French
- Weight
- 174 KB
- Volume
- 23
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
Eleven aromatic halides are reduced in very high yields in the presence of LiAlH4 and sonic waves at 35". Recently we have succeeded in accelerating the rates of several reactions using sonic waves.ls3 For example, the Wurtz-type coupling of organic halides, RX, (R = alkyl, aryl, benzyl and benzoyl and X = Cl, 8r and I)l and organometallic chlorides, R3MC1, (R = alkyl, aryl; M = Si Sn)* using lithium wire at room temperature proceeds at a convenient rate only in the presence of ultrasounds. We've also found that sonication of a dioxane solution of a,a'-dibromo-o-xylene in the presence of zinc powder provides an easy route to good yields of the reactive intermediate o-xylylene3 and that ultrasound facilitates the reaction of lithium with bis(mesityl)dichlorosilane to give good yields of tetramesityldisilene, a stable compound containing a silicon-silicon double bond.4 These observations, in conjunction with the earlier successful rate accelerations of the Barbier reaction 5 and mercury reduction of a,a'-dibromoketones,6 point to considerable synthetic potential for sonic waves in heterogeneous reactions. Applied to homogeneous systems , ultrasound has produced rate enhancements that are modest by comparison. 7 That aromatic halides are reluctant substrates for nucleophilic substitution is wellknown and it is generally accepted that electron-donating groups on the ring further impede displacement of the halogen. Nucleophilic hydrogen, however, in the form of complex metal hydrides, has been employed with some success in the reduction of aryl halides.8 Bromobenzene, for example, gave a 52% yield of benzene after 6 h and 95% after 24 h when treated with a four 1643